Hello @VIVE_chengnay,
OnApplicationPause(bool pause) was never called when I needed it.
As @Mark Moukarzel said, and as I have seen elsewhere on the forums, this is only called after 3 mins of the HMD being idle.
This does not fit my use case, so I'm currently using Interop.WVR_IsInputFocusCapturedBySystem() which seems to work fine.
Thank you both for your replies !